1. Field of the Invention
The present invention relates to an etching solution for a metal layer, and more particularly, to an etching solution for a copper-molybdenum layer and an etching method using the same.
2. Discussion of the Related Art
In general, in order to form a metal line on a substrate for a semiconductor device, several steps are required such as forming a metal layer on a substrate using sputtering, forming a photoresist (PR) pattern on the metal layer by coating, exposure and development and etching the metal layer with a cleaning step before and/or after each of the steps. The metal layer is patterned using the PR pattern as an etching mask during the etching step. A dry etching method using plasma or wet etching method using an etching solution may be used for the etching step.
Recently, the resistance of a metal layer has been an issue for semiconductor devices. Resistance of a metal layer is a crucial factor for a RC (resistance-capacitance) signal delay component in semiconductor devices. Likewise, resistance of metal layers should be considered to increase the panel size and resolution of thin film transistor liquid crystal display (TFT-LCD) devices. For a large-size TFT-LCD device, the RC signal delay should be reduced and a material having low resistivity should be developed. In general, metals such as chromium (Cr) (resistivity of about 12.7×10−8 Ωm), molybdenum (Mo) (resistivity of about 5×10−8 Ωm), aluminum (Al) (resistivity of about 2.65×10−8 Ωm) and alloys thereof have been used for the metal layers of TFT-LCD devices. However, those metals are not suitable for gate and data lines of a large-size TFT-LCD device due to their high resistance. As a result, copper (Cu) has been suggested as a material for a metal line. Copper (Cu) has a lower resistivity than aluminum (Al) and chromium (Cr), and has other advantages for the environment. However, copper has disadvantages with respect to the photolithographic process, which includes PR coating and patterning steps. Moreover, copper has a poor adhesion to an insulating layer including silicon (Si).
To overcome the disadvantages of a copper (Cu) single layer, a multiple layer including copper (Cu) has been suggested. For example, a multiple layer of copper (Cu) and titanium (Ti) has been evaluated as a metal line for a large-size TFT-LCD device. An etching solution for the multiple layer of copper (Cu) and titanium (Ti) has already exist and several other etching solutions have been suggested. However, since the etching solution for the multiple layer of copper (Cu) and titanium (Ti) includes fluoric ion due to a chemical property of titanium (Ti), layers having silicon in TFT-LCD devices (e.g., a glass substrate, an active layer of silicon, an insulating layer of silicon nitride (SiNx) or silicon oxide (SiO2)) are also etched. This undesired etching of the layers including silicon complicates the fabricating process of the TFT-LCD devices.
Accordingly, a multiple layer of copper (Cu) and molybdenum (Mo) is suggested. The multiple layer of copper (Cu) and molybdenum (Mo) may have properties equal to or better than the multiple layer of copper (Cu) and titanium (Ti) by controlling a thickness ratio. Moreover, since fluoric ions do not have a direct influence on the etching of the multiple layer of copper (Cu) and molybdenum (Mo), only a small amount of fluoric ions may be added to an etching solution for the multiple layer of copper (Cu) and molybdenum (Mo) such that a layer including silicon is not etched.
An etching solution including phosphoric acid, nitric acid and acetic acid for the multiple layer including copper (Cu) is disclosed in a published patent No. KP 1999-0017836, and an etching solution including iron chloride (III) hexa-hydride and hydrofluoric acid for a multiple layer including copper (Cu) is disclosed in a published patent No. KP 2000-0032999. However, when these etching solutions are used to etch a multiple layer of copper (Cu) and molybdenum (Mo), several drawbacks exist. First, etching speed is too high to control the etching step so that process margin is insufficient. Second, since a taper angle of the cross-sectional profile of the etched multiple layer is equal to or greater than about 90°, device defects or inferiority may occur during a subsequent process. Third, straightness of the etched multiple layer is not good. Fourth, when the etching solution including iron chloride (III) hexa-hydride and hydrofluoric acid is used, a layer including silicon is undesirably etched as in the case of the etching solution for a multiple layer of copper (Cu) and titanium (Ti).
FIG. 1A is a perspective scanning electron microscope (SEM) image showing a pattern of copper (Cu) and molybdenum (Mo) formed by etching with an etching solution including phosphoric acid, nitric acid and acetic acid, and FIG. 1B is a perspective scanning electron microscope (SEM) image showing a pattern of copper (Cu) and molybdenum (Mo) formed by etching with an etching solution including iron chloride (III) hexa-hydride and hydrofluoric acid. As shown in FIGS. 1A and 1B, the pattern of copper (Cu) and molybdenum (Mo) has a poor profile and a poor straightness. Especially, in FIG. 1B, the glass substrate has a rough top surface because hydrofluoric acid of the etching solution etches the glass substrate which includes silicon.
Another etching solution which includes hydrogen peroxide is suggested for etching a multiple layer of copper (Cu) and molybdenum (Mo). However, the etching solution has a first optimum pH value of about 2 to about 4 for copper (Cu) and a second optimum pH value of about 4 to about 7 for molybdenum (Mo). As a result, the molybdenum (Mo) layer may remain as a residue when the etching solution is controlled to have the first optimum pH value for copper (Cu), and etching speed of the copper (Cu) layer is severely reduced when the etching solution is controlled to have the second optimum pH value for molybdenum (Mo).
FIG. 2A is a cross-sectional scanning electron microscope (SEM) image showing a pattern of copper (Cu) and molybdenum (Mo) formed by etching with an etching solution including hydrogen peroxide, FIG. 2B is a perspective scanning electron microscope (SEM) image showing a pattern of copper (Cu) and molybdenum (Mo) formed by etching with an etching solution including hydrogen peroxide, and FIG. 2C is a perspective scanning electron microscope (SEM) image showing a substrate after etching with an etching solution including hydrogen peroxide. As shown in FIGS. 2A and 2B, the pattern of copper (Cu) and molybdenum (Mo) has a relatively good profile and a good straightness. As shown in FIG. 2C, however, a large number of molybdenum (Mo) residues are observed on the substrate because the etching solution having a pH value suitable for copper (Cu) does not etch molybdenum (Mo) completely.